1. Field of the Invention
The present invention relates to a power module structure and, more particularly, to a power module structure including a smoothing capacitor for smoothing a DC supply voltage to be externally applied to a power semiconductor device such as an IGBT.
2. Description of the Background Art
FIG. 28 is a schematic top plan view of a structure of a background art power module body portion 100. Output terminals 111U, 111V and 111W are arranged along a first side of a top surface of a case frame 106, and a P-terminal 108P and an N-terminal 108N are arranged along a second side of the top surface of the case frame 106 which is parallel to the first side.
FIG. 29 is a cross-sectional view showing a cross-sectional structure taken along the line X100xe2x80x94X100 of FIG. 28. The case frame 106 made of resin is disposed on a base plate 101 made of metal. A case lid 116 made of resin is disposed on the case frame 106. An insulating substrate 102 made of ceramic is soldered, as shown at 103, onto the base plate 101. A plurality of power semiconductor devices 105 such as IGBTs are soldered, as shown at 104, onto the insulating substrate 102. Circuit elements (not shown) such as switching elements are mounted on the top surface of the insulating substrate 102, and a predetermined circuit pattern (not shown) is formed on the top surface of the insulating substrate 102.
A control substrate 114 formed with a control circuit for controlling the power semiconductor devices 105 is disposed within the case frame 106. The control substrate 114 is soldered to first ends of respective interconnection electrodes 112. Second ends of the respective interconnection electrodes 112 are connected through aluminum wires 109 to the power semiconductor devices 105. An anti-noise shield plate 113 is disposed between the control substrate 114 and the insulating substrate 102 within the case frame 106. An interior space of the case frame 106 below the shield plate 113 is filled with a silicone gel 115.
The N-terminal 108N is disposed on the top surface of the case frame 106. The N-terminal 108N is connected to a first end of an N-electrode 107N. A second end of the N-electrode 107N is connected through the aluminum wires 109 to the power semiconductor devices 105. The P-terminal 108P (not shown in FIG. 29) is also disposed on the top surface of the case frame 106. The P-terminal 108P is connected to a first end of a P-electrode 107P. A second end of the P-electrode 107P is connected to the power semiconductor devices 105 through the aluminum wires 109 and the circuit pattern formed on the insulating substrate 102. The output terminal 111V is disposed on the top surface of the case frame 106. The output terminal 111V is connected to a first end of an output electrode 110. A second end of the output electrode 110 is connected through the aluminum wires 109 to the power semiconductor devices 105.
FIG. 30 is a schematic cross-sectional view showing the overall construction of a background power module, as viewed in side elevation. A smoothing capacitor 120 for smoothing a DC supply voltage to be externally applied to the power semiconductor devices 150 is disposed over the power module body portion 100. An N-electrode 121N and a P-electrode 121P (both designated by the reference numeral 121 in FIG. 30) of the smoothing capacitor 120, and the N-terminal 108N and the P-terminal 108P (both designated by the reference numeral 108 in FIG. 30) of the power module body portion 100 are connected to each other through a connecting conductor 124. The connecting conductor 124 has conductor plates 122N and 122P opposed to each other, with an insulation plate 123 therebetween. The conductor plates 122N, 122P and the N- and P-terminals 108N, 108P are fastened to each other with respective screws 125.
FIG. 31 is a schematic cross-sectional view showing a structure of connections between the smoothing capacitors 120 and the connecting conductor 124, as viewed in top plan. The conductor plate 122N is in contact with the N-electrodes 121N, and the conductor plate 122P is in contact with the P-electrodes 121P. The conductor plate 122N has openings 126 provided partially to avoid contact with the P-electrodes 121P, and the conductor plate 122P has openings 127 provided partially to avoid contact with the N-electrodes 121N.
However, the above-mentioned background art power module requires the connecting conductor 124 including the conductor plates 122N, 122P and the insulation plate 123 for connection between the N- and P-electrodes 121N, 121P of the smoothing capacitors 120 and the N- and P-terminals 108N, 108P of the power module body portion 100. This presents problems in the large number of parts and in complicated assembly.
Another problem is an increased circuit inductance because of a long wiring path between the smoothing capacitors 120 and the power semiconductor devices 105. In the operation of the power module, the high-speed switching of the power semiconductor devices 105 causes a large pulse-shaped current proportional to the amount of current change (di/dt) to flow between the smoothing capacitors 120 and the power semiconductor devices 105, thereby to develop a voltage proportional to the circuit inductance, which in turn is applied as noise to the power semiconductor devices 105. Further, the increase in circuit inductance requires the increase in electrostatic capacitance of the smoothing capacitors 120 for suppression of ripple voltage. This results in the increase in the size of the smoothing capacitors 120 and accordingly the increase in the size of the power module itself. Therefore, the circuit inductance is preferably low.
Furthermore, the background art power module which comprises the large-sized smoothing capacitors 120 disposed over the power module body portion 100 is too low in resistance to vibration for use as a vehicle-mounted power module, for example.
According to a first aspect of the present invention, a power module comprises: a substrate with a power semiconductor device mounted thereon; a case having an interior in which the substrate is disposed; an N-terminal and a P-terminal arranged along a first side of a main surface of the case and electrically connected to the power semiconductor device; and a smoothing capacitor having a first electrode connected to the N-terminal and a second electrode connected to the P-terminal for smoothing a voltage to be externally supplied to the power semiconductor device, wherein the smoothing capacitor has a main surface level with the main surface of the case, and is disposed in contact with a side surface of the case including the first side of the main surface of the case, and wherein the first electrode and the second electrode are disposed on the main surface of the smoothing capacitor and in proximity to the N-terminal and the P-terminal, respectively.
Preferably, according to a second aspect of the present invention, in the power module of the first aspect, the smoothing capacitor comprises: an enclosure; a plurality of capacitor elements disposed in the enclosure, each of the plurality of capacitor elements having a first electrode abutting against the first electrode of the smoothing capacitor and a second electrode abutting against the second electrode of the smoothing capacitor; and a hold-down plate for pressing the plurality of capacitor elements against the enclosure to fix the plurality of capacitor elements in the enclosure.
Preferably, according to a third aspect of the present invention, in the power module of the second aspect, the enclosure has a single heat sink for dissipating heat generated by the plurality of capacitor elements.
Preferably, according to a fourth aspect of the present invention, in the power module of the second or third aspect, at least one of the first and second electrodes of the smoothing capacitor has elasticity.
According to a fifth aspect of the present invention, a power module comprises: a substrate with a power semiconductor device mounted thereon; a case having an interior in which the substrate is disposed, the case including a predetermined recess in an outer surface thereof; an N-terminal and a P-terminal disposed on side walls of the recess and electrically connected to the power semiconductor device; and a smoothing capacitor fitted in the recess and having a first electrode positioned to correspond to the N-terminal and a second electrode positioned to correspond to the P-terminal for smoothing a voltage to be externally supplied to the power semiconductor device.
Preferably, according to a sixth aspect of the present invention, in the power module of the fifth aspect, there is provided at least one of a first electrically conductive elastic member between the first electrode and the N-terminal and a second electrically conductive elastic member between the second electrode and the P-terminal.
According to a seventh aspect of the present invention, a power module comprises: a first substrate with a power semiconductor device mounted thereon; a second substrate with a control circuit for controlling the power semiconductor device formed thereon; a smoothing capacitor electrically connected to the power semiconductor device for smoothing a voltage to be externally supplied to the power semiconductor device; and a case including a case frame and a case lid, the case having an interior in which the first substrate, the second substrate and the smoothing capacitor are disposed.
Preferably, according to an eighth aspect of the present invention, in the power module of the seventh aspect, the smoothing capacitor is disposed on the case lid.
Preferably, according to a ninth aspect of the present invention, the power module of the seventh aspect further comprises a shield plate disposed between the first substrate and the second substrate and fixed to the case frame, wherein the smoothing capacitor is disposed on the shield plate.
Preferably, according to a tenth aspect of the present invention, the power module of the ninth aspect further comprises a thermally conductive sheet formed between the shield plate and the smoothing capacitor.
Preferably, according to an eleventh aspect of the present invention, in the power module of the ninth aspect, the shield plate is a metal shield plate.
Preferably, according to a twelfth aspect of the present invention, in the power module of the seventh aspect, the smoothing capacitor is disposed on the first substrate.
Preferably, according to a thirteenth aspect of the present invention, in the power module of the twelfth aspect, the first substrate and the smoothing capacitor are made of the same material.
Preferably, according to a fourteenth aspect of the present invention, the power module of the seventh aspect further comprises a heat sink for dissipating heat generated from the first substrate, the first substrate and the case frame being placed on the heat sink, wherein the smoothing capacitor is disposed on the heat sink.
According to a fifteenth aspect of the present invention, a power module comprises: a substrate with a power semiconductor device mounted thereon; a case having an interior in which the substrate is disposed; a cooling fin having a surface on which the substrate and the case are placed; and a smoothing capacitor disposed on an opposite surface of the cooling fin from the surface on which the substrate is placed, the smoothing capacitor being electrically connected to the power semiconductor device for smoothing a voltage to be externally supplied to the power semiconductor device.
Preferably, according to a sixteenth aspect of the present invention, in the power module of any one of the first to fifteenth aspects, the smoothing capacitor is a ceramic capacitor.
The power module according to the first aspect of the present invention can shorten the wiring path between the smoothing capacitor and the power semiconductor device to reduce a circuit inductance. The contacting relationship between a side surface of the smoothing capacitor and the side surface of the case increases resistance to vibration.
In the power module according to the second aspect of the present invention, the hold-down plate collectively fixes the plurality of capacitor elements in the enclosure. This facilitates the step of mounting the plurality of capacitor elements.
The power module according to the third aspect of the present invention enhances the uniformity of the effect of cooling the plurality of capacitor elements.
The power module according to the fourth aspect of the present invention can prevent breakage of the capacitor elements resulting from the pressing force of the hold-down plate or the thermal stress associated with heat generated by the capacitor elements. Additionally, the power module according to the fourth aspect of the present invention can ensure the contact between the first electrode of the smoothing capacitor and the first electrodes of the respective capacitor elements and between the second electrode of the smoothing capacitor and the second electrodes of the respective capacitor elements.
The power module according to the aspect of the present invention can shorten the wiring path between the smoothing capacitor and the power semiconductor device to reduce the circuit inductance. The provision of the smoothing capacitor fitted in the recess of the case reduces the size of the power module.
The power module according to the sixth aspect of the present invention can prevent breakage of the smoothing capacitor resulting from the pressing force exerted when the smoothing capacitor is inserted into the recess or the thermal stress associated with the heat generated by the smoothing capacitor. Additionally, the power module according to the sixth aspect of the present invention can ensure the contact between the N-terminal and the first electrode of the smoothing capacitor and between the P-terminal and the second electrode of the smoothing capacitor.
The power module according to the seventh aspect of the present invention can improve environmental resistance since the smoothing capacitor is isolated from an environment external to the case.
The power module according to the eighth aspect of the present invention can dissipate the heat generated by the smoothing capacitor through the case lid to the outside.
The power module according to the ninth aspect of the present invention has a shorter wiring path between the smoothing capacitor and the power semiconductor device than that of the power module according to the eighth aspect, to further reduce the circuit inductance.
The power module according to the tenth aspect of the present invention can effectively dissipate the heat generated by the smoothing capacitor through the thermally conductive sheet and the case frame to the outside, and alleviate the stress associated with the heat generated by the smoothing capacitor.
The power module according to the eleventh aspect of the present invention can effectively dissipate the heat generated by the smoothing capacitor through the shield plate and the case frame to the outside.
The power module according to the twelfth aspect of the present invention can significantly shorten the wiring path between the smoothing capacitor and the power semiconductor device to greatly reduce the circuit inductance.
The power module according to the thirteenth aspect of the present invention can make the smoothing capacitor and the insulating substrate equal in thermal expansion coefficient, to avoid various disadvantages resulting from the difference in thermal expansion coefficient, thereby enhancing the reliability of the power module.
The power module according to the fourteenth aspect of the present invention can effectively dissipate the heat generated by the smoothing capacitor through the heat sink to the outside.
In the power module according to the fifteenth aspect of the present invention, the cooling fin can effectively cool down the smoothing capacitor to enhance the reliability of the power module.
In the power module according to the sixteenth aspect of the present invention, the use of the ceramic capacitor having good charging and discharging properties increases the operating speed of the power module.
It is therefore an object of the present invention to provide a power module which can reduce a circuit inductance and which is small in size, light in weight and high in resistance to vibration.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.